A typical printed circuit board comprises conductive tracks, usually together with other circuit components, carried by an electrically insulating board. Often, holes extend from one surface of the board to the other and have plated surfaces to permit electrical connections to be made through them. If part of a circuit is damaged, it can often be difficult to effect repairs without causing additional damage to other parts of the circuit. For example, if a hole must be replated, it is difficult to ensure that any replating is confined solely to the desired regions. Also, parts of the circuit may become damaged when they are masked to prevent contamination by plating solutions.